1. Field of the Invention
The present invention relates to an image processing apparatus and an imaging system.
2. Description of the Related Art
A solid-state imaging apparatus, such as a CMOS image sensor and a CCD image sensor, has a structure in which a color separation filter is laminated over a pixel cell including a photoelectric conversion element, and a condenser lens is further laminated over the color separation filter. In a color solid-state imaging apparatus having the structure, the photoelectric conversion element and the condenser lens are separated by a color filter and a plurality of insulating films. Particularly, a CMOS image sensor includes a plurality of wiring layers on pixels, and the distance between the photoelectric conversion element and the condenser lens is greater than that in the CCD image sensor. Therefore, in a path until light passing through a color filter of a photoelectric conversion element reaches the photoelectric conversion element, components of the light entering adjacent photoelectric conversion elements of other colors cannot be ignored. The components are called a cross talk. The cross talk is not only caused by an optical reason, but, for example, there are components that pass through a photoelectric conversion element of a pixel, and a photoelectric charge leaks to adjacent pixels inside silicon. Even if the light is absorbed by a photoelectric conversion element of a pixel and converted to an electric charge, there are components in which the electric charge diffuses inside the semiconductor and drifts and leaks to adjacent pixels. The components have a characteristic of enlarging as the size of one pixel is reduced. There is a known technique of subtracting a certain ratio of signal components calculated based on signals of pixels that are adjacent to a specific color pixel and that have colors other than the specific color to correct cross talk components by signal processing (Japanese Patent Application Laid-Open No. 2004-135206). There is also a known technique for reducing the cross talk by changing the amount of subtraction according to pixels in different colors in consideration of the asymmetry caused by a layout of wiring of pixels (Japanese Patent Application Laid-Open No. 2007-142697).
The techniques of Japanese Patent Application Laid-Open No. 2004-135206 and Japanese Patent Application Laid-Open No. 2007-142697 effectively function when the pixel size is relatively large. However, if the pixel size is reduced, there would be ununiformity and variation in color mixing (cross talk) quantity depending on the position on the imaging region. Although the incident light perpendicularly enters at the center of the imaging region, the incident light diagonally enters the imaging surface near the edge of the imaging region. The direction and the extent of the inclination also vary depending on the position on the imaging region. The cross talk increases if the pixel size is reduced, and from which color of pixel of up, down, left, and right pixels and how much the cross talk signal is superimposed significantly vary depending on the structure and the layout of the pixels. In Japanese Patent Application Laid-Open No. 2004-135206 and Japanese Patent Application Laid-Open No. 2007-142697, the amount of correction is constant regardless of the position on the imaging region. Therefore, satisfactory correction on all positions on the imaging surface is difficult.
An object of the present invention is to provide an image processing apparatus and an imaging system capable of realizing suitable cross talk correction throughout the entire region of the imaging region.